The present invention relates to the hard disc drive industry, and in particular to read/write preamplifiers having the capability of simultaneously writing servo information to multiple heads.
A read/write inductive disc drive head in a hard disc drive performs two specific functions. First, the head accepts a magnetic transmission signal from the disc drive and writes the signal to a magnetic disc medium during a write mode. This function requires large currents and voltages (approximately 40 milliamperes per head at 5 volts). Second, the disc drive head reads magnetic transmission signals from the disc during a read mode, requiring relatively small voltages and currents.
Properly positioning a disc drive head over a specific magnetic data track on a disc is critical for high performance of the system. An important function of the disc drive during either a read or write application is the extraction of a position error signal, which indicates that the head is incorrectly positioned over a desired magnetic-data track. An incorrectly positioned head can result in magnetic signals or information being erroneously written to or read from the disc.
A recent development in the hard disc drive industry is the concept of servo fields. Servo fields, also called servo information or servo bursts, are pre-written patterned feedback information positioned at particular sections of a disc. Servo fields are examined and utilized to determine whether a disc drive head is accurately positioned over a desired magnetic data track. If the head is not properly positioned over a desired track, the servo fields provide a feedback signal which keeps the head on track during a read or write application.
During a read or write application, a position error signal may develop indicating that the head is incorrectly positioned over a desired magnetic-data track. The position error signal is proportional to the deviation of the head from the center of the desired magnetic data track. The servo fields recognize the position error of the head and apply electromechanical negative feedback to the head to force the head position to the center of the desired track. This feedback control loop is one of the key features of a Winchester disc drive since the track-following servo fields allow the head to be correctly positioned independent of such mechanical problems as vibration, bearing rattle and wobble, mechanical "backlash" and "runout," non-circularity of the track, thermal expansion, and wear. In addition, it makes the precision requirements of mechanical components within the disc drive much less rigorous and generally results in a cheaper, denser storage unit.
In contrast to hard discs, servo fields are not necessary when using a floppy disc and a floppy disc drive because of the low density of floppy discs. A floppy disc has a relatively low number of tracks per disc, as compared to a hard disc; therefore, a disc drive head can be accurately positioned over a given magnetic data track without the use of servo fields or electromechanical negative feedback. However, hard discs have a much greater density than floppy discs. This high density is achieved by placing the magnetic data tracks of a hard disc substantially closer together than the data tracks of a floppy disc. This high density necessitates the need for a feedback system, i.e., servo fields, to determine whether the disc drive head is accurately positioned over a desired magnetic data track.
Since the inception of servo fields, hard disc drive manufacturers would pre-write the necessary servo fields to one surface of one disc at a time. The servo fields would first be written to one surface of the disc, and then written to the other surface of the disc. This procedure is repeated for virtually every hard disc presently being manufactured and is extremely time consuming. Disc drive manufactures have found that the additional procedure of writing servo fields to their magnetic discs in addition to writing standard data information to the magnetic discs greatly inhibits the disc manufacturing process. However, writing servo fields and data information to too many disc surfaces at one time dissipates too much power and causes the integrated circuits within the disc drive heads to overheat and fail.
Therefore, there is a need for a system which has the capability of simultaneously writing servo information to a plurality of magnetic discs in a servo write mode, and for writing data to the plurality of magnetic discs in a data write mode.